Don't connect AREF to Vcc, it'll may be damaged. Just have a decoupling cap to ground from this pin.

Just curious, why do we connect a cap there?

Because that pin is connected internally to the reference voltage used for the A/D converter used for analogRead() statements. So the extra noise filtering from the cap will help improve the accuracy of the A/D measurements.

The cap helps keep noise from the reference and therefore is often used to get cleaner analog readings.

When using one of the INTERNAL options AREF is actually connected to this internal reference, if it is also connected to say 5v you have 5v->1.1v (or whatever is selected) which is bad.

You can connect Vs to AREF but have to be very careful never to use an INTERNAL reference.

______Rob

Actually the Arduino reference has instructions on wiring a series resistor between the Aref pin and any external voltage reference being used. That would prevent damaging current level flows in case of misuse of the analog reference command. http://arduino.cc/en/Reference/AnalogReference